This invention relates generally to a new and improved electromagnetic lock system for providing controlled access through a doorway by means of an electromagnetic lock. More particularly, this invention relates to a lock system wherein controlled access through a doorway is accomplished by means of an automatic electronic sensor system.
Electromagnetic locks which function to magnetically bond a door to the door frame have proved very advantageous in satisfying both security and safety requirements and in providing efficient and reliable means for remote control and monitoring of doorways of a multi-lock system. Electromagnetic locks have effectively eliminated numerous mechanical limitations of the mechanical lock system and have gained widespread popularity. The many additional advantages of electromagnetic lock systems over the conventional mechanical-type lock system, such as centralized control and monitoring, ease of installation and ease of maintenance due to the absence of moving parts are now well established.
In U.S. Pat. No. 4,763,937, entitled "Electromagnetic Door Lock System", an electromagnetic door lock system employs an electromagnetic lock which magnetically bonds with an armature plate. An acoustical transducer generates an ultrasonic detection beam which is directed toward the doorknob. Reflected energy is received and electronically processed to detect the presence of a foreign object such as a hand in the vicinity of the doorknob. The lock automatically de-actuates when the foreign object is detected. The electromagnetic lock sensor and processing circuitry are mounted in a housing which is located near the top of a doorway. Electromagnetic locks such as disclosed in U.S. Pat. No. 4,763,937 are adaptable for use in providing controlled access through a multiplicity of stairwell doors in multi-story structures. Such lock systems also incorporate means for controlling authorized egress and for discriminating against unauthorized egress through the doorways. In addition, the electromagnetic locks are adapted for use with a centralized supervisory remote control and remote monitoring to enhance the multi-lock security system and may also be integrated with a smoke detection system.
Although electromagnetic locks such as disclosed in U.S. Pat. No. 4,763,937 reliably operate in an efficient manner under a wide variety of operational conditions, the use of a single detection system, such as an ultrasonic detection system, may under certain conditions, be susceptible to false readings. For example, objects which are mounted off of the floor, may reflect a signal back to the electromagnetic lock receiver in such a form that the processing circuitry is unable to discriminate between the fixed object and that of a human entering the detection zone. Plants, drapes, fire extinguishers etc., under certain conditions are known to produce false detector readings. In addition, certain frequency range noise in close proximity to the lock, such as, for example, noise originating from certain machining processes or air hoses, may cause the lock to release. Crossing traffic in close proximity to the door may also cause the lock to inappropriately automatically release. In addition, cross-talk between closely adjacent locks may result in at least one of the locks releasing.
Accordingly, it is a general aim of the present invention to provide a new and improved electromagnetic lock system which employs a dual sensing system to increase the accuracy and reliability of the automatic locking system and enhance the ability of the system to discriminate between invalid and valid lock release stimuli.